1. Field of the Invention:
The present invention relates to reinforcing metal fibers, such as steel fibers, to be mixed in concrete or a refractory material to improve the physical properties of concrete or a refractory material.
2. Description of the Prior Art:
It has been common practice to mix metal fibers in concrete at a metal fiber content of 1 to 2% by volume in order to improve the strength and toughness of concrete structures. In most cases, such metal fibers are made of steel because of its low cost and high strength. Japanese Patent Provisional Publication (Kokai) No. 60-221224 discloses exemplary recent art relating to the present invention.
If a large quantity of metal fibers are supplied into concrete in a short time to save time for preparing fiber reinforced concrete, the metal fibers are liable to be entangled with each other resulting in the formation of fiber balls, and thereby the metal fibers are dispersed irregularly in the concrete Such irregular dispersion of the metal fibers in the concrete is unable to provide sufficient concrete reinforcing effect, and hence the fiber reinforced concrete has insufficient strength and toughness, and the required improvement of the physical properties can not be achieved, which is obvious from the bending load-deflection characteristic curve C in FIG. 1.
Such a problem can tentatively be solved by the use of a fiber dispersing machine, which is as heavy as over 100 kg, at the concrete mixing site during concrete mixing operations. However, the dispersing machine requires additional space for installation, additional maintenance work, and furthermore deteriorates working efficiency in mixing concrete.
It has been known that metal fibers whose tensile strength and bonding strength with concrete are well balanced can produce the most efficient concrete reinforcing effects. Efforts have been made to improve the concrete reinforcing characteristics of metal fibers through examinations on the influence of the aspect ratio on them. The aspect ratio is defined as l/d, where l is the length of a metal fiber and d is its equivalent diameter.
Basically, the section of the conventional metal fiber is round or square because of the availability of materials. To enhance the bonding strength of a metal fiber without changing the length thereof, it has been common practice to corrugate or indent the metal fiber along its entire length. However, the dispersibility of the metal fiber has not yet been improved satisfactorily and hence the dispersing machine has been used.